1. Field of the Invention
The present invention pertains to apparatus for supporting and manipulating equipment. More particularly, the present invention relates to support apparatus of the type utilizing blocks and lines, such as a traveling block, to which equipment may be connected, and a crown block from which the traveling block is suspended by means of a line arrayed between sheaves forming parts of the two blocks. The present invention finds particular application in environments wherein such block arrangements are supported by floating vessels and used to manipulate equipment relative to the floor of the body of water supporting the vessel, or in environments wherein soft landings of equipment are desired.
2. Description of Prior Art
Motion compensators are known for compensating for the vertical heaving of marine vessels supporting submerged equipment during drilling or other undersea well operations. Such compensators include traveling block compensators wherein a hook, elevator or the like by which equipment may be connected to a traveling block is suspended from the traveling block by means of fluid pressure assemblies which reciprocate to allow the hook to be maintained fixed relative to the undersea floor as the traveling block heaves with the derrick and floating vessel due to wave action for example. Such compensators require the weight of the compensation apparatus to be supported by the same line by which the traveling block is suspended from the crown block, which is fixed to the mast or derrick.
A motion compensator wherein the crown block is intended to remain stationary relative to the undersea floor as the derrick and floating vessel heaves has been designed whereby the crown block is supported from the derrick by means of a pair of direct-acting hydraulic piston-and-cylinder assemblies. However, additional compensation apparatus is required in that case to eliminate linear movement of the flexible line supporting the traveling block to prevent relative motion between the traveling block and the crown block as a result of heaving of the derrick.
It is desirable and advantageous to provide a crown block compensator supported from fluid pressure assemblies providing balanced support and positioned to minimize the required height of a derrick or mast supporting the crown block and traveling block combination. Similarly, it is desirable to provide like compensation to the line interconnecting the two blocks so that the traveling block and the crown block may remain stationary relative to the undersea floor as the derrick is heaved with the floating vessel with no additional compensation assemblies. The height of the derrick may be so minimized also by providing a mechanical advantage with the crown block compensator assemblies so that relatively large heave of the derrick may be compensated with lesser relative movement between the compensator assembly components.